Liquid jetting device

ABSTRACT

A liquid jetting apparatus ( 20 ) to jet a droplet of a charged liquid solution onto a base material, having: a nozzle ( 21 ) in which an edge portion thereof is arranged to face the base material K having a receiving surface to receive the jetted droplet, and an inside diameter of the edge portion from which the droplet is jetted is not more than 30 [μm]; a liquid solution supplying section ( 29 ) to supply the liquid solution into the nozzle ( 21 ); a jetting voltage applying section ( 25 ) to apply a jetting voltage to the liquid solution in the nozzle ( 21 ); and a convex meniscus forming section ( 40 ) to form a state where the liquid solution in the nozzle ( 21 ) protrudes from the nozzle edge portion.

CROSS REFERENCE TO RELATED APPLICATION

This is a U.S. national stage of application No. PCT/JP2003/012099,filed on 22 Sep. 2003. Priority under 35 U.S.C. §119(a) and 35 U.S.C.365(b) is claimed from Japanese Application No. 2002-278231, filed 24Sep. 2002 and Japanese Application No. 2003-293043, filed 13 Aug. 2003,the disclosures of which are also incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a liquid jetting apparatus for jettingliquid to a base material.

BACKGROUND ART

As a conventional inkjet recording method, a piezo method for jetting anink droplet by changing a shape of an ink passage according to vibrationof a piezoelectric element, a thermal method for making a heat generatorprovided in an ink passage heat to generate air bubbles and jetting anink droplet according to a pressure change by the air bubbles in the inkpassage, and an electrostatic sucking method for charging ink in an inkpassage to jet an ink droplet by a electrostatic sucking power of theink are known.

An ink jet printer described in JP-Tokukaihei-11-277747 is cited as aconventional electrostatic sucking type ink jet printer. The ink jetprinter comprises a plurality of convex ink guides for jetting ink froman edge portion thereof, a counter electrode which is arranged to facethe edge of each ink guide and is grounded, and a jetting electrode forapplying a jetting voltage to ink for each ink guide. Two kinds of theconvex ink guides with different widths of slits to guide ink areprepared to have a feature to be able to jet an ink droplet with twokinds of sizes by appropriately using them.

The conventional ink jet printer jets an ink droplet by applying a pulsevoltage to the jetting electrode, and guides the ink droplet to thecounter electrode side by electric field formed between the jettingelectrode and the counter electrode.

However, the above-mentioned inkjet recording method has the followingproblems.

(1) Limit and Stability of a Minute Liquid Droplet Formation

Since a nozzle diameter is large, a shape of a droplet jetted from anozzle is not stabilized, and there is a limit of making a dropletminute.

(2) High Applying Voltage

For jetting a minute droplet, miniaturization of a jet opening of thenozzle is an important factor. In a principle of the conventionalelectrostatic sucking method, since the nozzle diameter is large,electric field intensity of a nozzle edge portion is weak, andtherefore, in order to obtain necessary electric field intensity forjetting a droplet, it is necessary to apply a high jetting voltage (forexample, extremely high voltage near 2000 [V]). Accordingly, in order toapply a high voltage, a driving control of a voltage becomes expensive.

Moreover, in the patent document 1 as the conventional example, inkjetting is performed only by applying a pulse voltage to the ink, so ahigh voltage needs to be applied to the electrode to which the pulsevoltage is applied. Thus, there is a disadvantage to accelerate theabove (2) and (3) problems.

Thereupon, to provide a liquid jetting apparatus capable of jetting aminute droplet is a first object. At the same time, to provide a liquidjetting apparatus capable of jetting a stable droplet is a secondobject. Further, to provide a liquid jetting apparatus which can reducean applying voltage and is cheap is a third object.

DISCLOSURE OF THE INVENTION

The present invention has a structure in which the liquid jettingapparatus to jet a droplet of a charged liquid solution onto a basematerial, comprises:

a liquid jetting head comprising a nozzle to jet the droplet from anedge portion, an inside diameter of the edge portion of the nozzle beingnot more than 30 [μm];

a liquid solution supplying section to supply the liquid solution intothe nozzle;

a jetting voltage applying section to apply a jetting voltage to theliquid solution in the nozzle; and

a convex meniscus forming section to form a state where the liquidsolution in the nozzle protrudes from the nozzle edge portion.

Hereinafter, the nozzle diameter indicates the inside diameter of thenozzle at the edge portion from which a droplet is jetted (insidediameter at the edge portion of the nozzle). A shape of cross section ofa droplet jetting hole in the nozzle is not limited to a round shape.For example, in the case where the cross-sectional shape of the liquidjetting hole is a polygon shape, a star-like shape or other shape, itindicates that the circumcircle of the cross-sectional shape is not morethan 30 [μm]. Hereinafter, regarding to the nozzle diameter or theinside diameter at the edge portion of the nozzle, it is to be the sameeven when other numerical limitations are given. The nozzle radiusindicates the length of ½ of the nozzle diameter (inside diameter of theedge portion of the nozzle).

In the present invention, “base material” indicates an object to receivelanding of a droplet of the liquid solution jetted, and material thereofis not specifically limited. Accordingly, for example, when applying theabove structure to the ink jet printer, a recording medium such as apaper, a sheet or the like corresponds to the base material, and whenforming a circuit by using a conductive paste, the base on which thecircuit is to be made corresponds to the base material.

In the above structure, the nozzle or the base material is arranged sothat a receiving surface where a droplet lands faces the edge portion ofthe nozzle. The arranging operation to realize the positional relationwith each other may be performed by moving either the nozzle or the basematerial.

Then, the liquid solution is supplied to the inside of the liquidjetting head by the liquid solution supplying section. The liquidsolution in the nozzle needs to be in a state of being charged forperforming jetting. An electrode exclusively for charging may beprovided to apply a voltage needed to charge the liquid solution.

The convex meniscus forming section forms a state where the liquidsolution protrudes at the nozzle edge portion (convex meniscus). Forforming the convex meniscus, for example, a method such as increasing apressure in the nozzle to be in the range that a droplet does not dropfrom the nozzle edge portion is adopted.

Then, before or at the same time of forming the convex meniscus at thenozzle edge portion, the jetting voltage at the position of the convexmeniscus is applied to the liquid solution in the liquid jetting head bythe jetting voltage applying section. This jetting voltage is set to bein the range where jetting of a droplet is not performed alone, but canbe performed in cooperation with the meniscus formation by the convexmeniscus forming section. Accordingly, when the convex meniscus isformed at the nozzle edge by the driving voltage for forming the convexmeniscus, a droplet of the liquid solution flies from the protrudingedge portion of the convex meniscus in a direction perpendicular to thereceiving surface of the base material, thereby forming a dot of theliquid solution on the receiving surface of the base material.

In the present invention, since the convex meniscus forming section isprovided, it is possible to focus the point to jet a droplet to the topof the convex meniscus, and a droplet can be jetted with a smallerjetting force than that in the case where the liquid level is flat orconcave. Thus, by actively utilizing the reduction of the jettingvoltage by smoothly jetting a droplet and the difference of the jettingvoltage depending upon the position of the meniscus, the jetting voltagecan be further reduced.

Conventionally, both of the convex meniscus formation and jetting adroplet are performed by applying a voltage to the liquid solution, sothat high voltage for performing both of them at the same time isrequired. However, in the present invention, the convex meniscusformation is performed by the convex meniscus forming section which isdifferent from the jetting voltage applying section for applying avoltage to the liquid solution, and jetting of a droplet is performed byapplying a voltage by the jetting voltage applying section, so that avoltage value applied to the liquid solution at the time of jetting canbe reduced.

Further, in the present invention, the electric field intensity becomeshigh by concentrating the electric filed at the nozzle edge portion withthe use of the nozzle having a super minute diameter which cannot befound conventionally, and at that time, an electrostatic force which isgenerated between the distance to an image charge on the base materialside is induced, thereby a droplet flies.

Accordingly, jetting a droplet can be performed with a lower voltagethan that which has been conventionally considered, even with the minutenozzle, and can be favorably performed even when the base material ismade of conductive material or insulating material.

In this case, jetting a droplet can be performed even when there is nocounter electrode facing the edge portion of the nozzle. For example, inthe case that the base material is arranged to face the nozzle edgeportion in the state where there is no counter electrode, when the basematerial is a conductor, an image charge with reversed polarity isinduced at a position which is plane symmetric with the nozzle edgeportion with respect to the receiving surface of the base material as astandard, and when the base material is an insulator, an image chargewith reversed polarity is induced at a symmetric position which isdefined by dielectric constant of the base material with respect to thereceiving surface of the base material as a standard. Flying of adroplet is performed by an electrostatic force between the electriccharge induced at the nozzle edge portion and the image charge.

Thereby, the number of components in the structure of the apparatus canbe reduced. Accordingly, when applying the present invention to abusiness ink jet system, in can contribute to improvement ofproductivity of the whole system, and also the cost can be reduced.

However, although the structure of the present invention can eliminatethe use of a counter electrode, the counter electrode may be used at thesame time. When the counter electrode is used at the same time,preferably, the base material is arranged to be along the facing surfaceof the counter electrode and the facing surface of the counter electrodeis arranged to be perpendicular to a direction of jetting a droplet fromthe nozzle, thereby it becomes possible to use an electrostatic force bythe electric field between the nozzle and the counter electrode forinducing a flying electrode. Moreover, by grounding the counterelectrode, an electric charge of a charged droplet can be released viathe counter electrode in addition to discharging the electric charge tothe air, so that the effect to reduce storage of electric charges canalso be obtained. Thus, using the counter electrode at the same time canbe described as a preferable structure.

In addition to the above structure, an operation control section tocontrol the respective applications of the driving voltage for drivingthe convex meniscus forming section and a jetting voltage by the jettingvoltage applying section may be provided, and this operation controlsection may have a structure to comprise a first jetting control unitfor controlling the application of the driving voltage of the convexmeniscus forming section when jetting a droplet while controlling theapplication of the jetting voltage by the jetting voltage applyingsection.

In this structure, by forming the convex meniscus according to the needof jetting in the state where the jetting voltage is preliminary appliedto the liquid solution by the first jetting control unit, theelectrostatic force necessary for jetting a droplet from the edgeportion of the nozzle can be obtained, thereby jetting a droplet isperformed.

In addition to the above structure, an operation control section tocontrol an application of the driving voltage of the convex meniscusforming section and a application by the jetting voltage applyingsection may be provided, and this operation control section may have astructure to comprise a second jetting control unit for performing aprotruding operation of the liquid solution by the convex meniscusforming section and the application of the jetting voltage insynchronization with each other.

In this structure, the second jetting control unit performs forming theconvex meniscus and jetting a droplet in synchronization with eachother, so that jetting a droplet by applying the jetting voltage as wellas forming the convex meniscus can be performed, thereby shortening thetime interval between the two operations.

Here, the above described “synchronization” includes not only the casewhere the period in which the protruding operation of the liquidsolution is performed accords with the period to apply the jettingvoltage in regard to the timing, but also the case where at least theperiod necessary for jetting a droplet overlaps even if there is adifference in the start and end timings between the one period and theother period.

Moreover, in addition to the above described respective structure, theoperation control section may comprise a liquid stabilization controlsection to perform an operation control to draw a liquid level at thenozzle edge portion to an inside after the protruding operation of theliquid solution and the application of the jetting voltage.

In this structure, after jetting a droplet, the droplet at the nozzleedge portion is sucked to the inside, for example, by reducing theinternal pressure of the nozzle or the like. When a droplet flies fromthe convex meniscus, the convex meniscus may vibrate due to the flyingof the droplet, and this case causes the need to perform the nextjetting after waiting the vibration of the convex meniscus to stop toprevent the effect of the vibration. In the above structure, even whenthe convex meniscus vibrates, because the convex state once disappearsby temporary sucking the liquid level at the nozzle edge portion to theinside of the nozzle, and also because of the rectification by passingthe inside of the nozzle with lower conductance, the liquid levelvibration state is resolved. Accordingly, the vibration of the liquidlevel is actively and promptly stopped, so that the next operations offorming the convex meniscus and jetting can be performed without waitinga certain waiting time for the vibration to stop after sucking like theconventional one.

Moreover, in addition to the above described structure, the convexmeniscus forming section may comprise a piezo element to change acapacity in the nozzle.

In this structure, the formation of the convex meniscus is performed sothat the piezo element changes the capacity in the nozzle by changingthe shape thereof to increase the nozzle pressure.

Drawing the liquid level at the nozzle edge portion to the inside isperformed so that the capacity in the nozzle is changed by the shapechange of the piezo element to decrease the nozzle pressure. By formingthe convex meniscus by the capacity change of the piezo element, thereis no limitation to the liquid solution and it is possible to drive athigh frequency.

Moreover, in addition to the above described structure, the convexmeniscus forming section may comprise a heater to generate an air bubblein the liquid solution in the nozzle.

In this structure, the formation of the convex meniscus is performed sothat air bubbles are formed by evaporation of the liquid solution withthe heat of the heater to increase the nozzle pressure. In the presentinvention, in principle, the jetting liquid solution is limited,however, structurally, it is simple, excellent in arranging nozzles inhigh density, and is sufficient for environmental responsiveness incomparison to the case of using a driving element such as a piezoelement or an electrostatic actuator.

Moreover, in addition to the above described structure, the structuremay be such that the jetting voltage applying section applies a jettingvoltage V satisfying the following equation (1).

$\begin{matrix}{{h\sqrt{\frac{\gamma\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2\; ɛ_{0}}}} & (1)\end{matrix}$where, γ: surface tension of liquid solution [N/m], ε₀: electricconstant [F/m], d: nozzle diameter [m], h: distance between nozzle andbase material [m], k: proportionality constant dependent on nozzle shape(1.5<k<8.5).

In this structure, the jetting voltage V in the range of the aboveequation (1) is applied to the liquid solution in the nozzle. In theabove equation (1), the left term as a standard of the upper limit ofthe jetting voltage V indicates the lowest limit jetting voltage in thecase of performing jetting a droplet by the electric field between thenozzle and the counter electrode of the conventional one. In the presentinvention, as described above, by the effect of the electric fieldconcentration due to the super miniaturization of the nozzle, jetting asuper minute droplet can be realized even if the jetting voltage V isset to be lower than the conventional lowest limit jetting voltage,which was not realized by the conventional technique.

In the above equation (1), the right term as a standard of the lowerlimit of the jetting voltage V indicates the lowest limit jettingvoltage of the present invention for jetting a droplet against thesurface tension by the liquid solution at the nozzle edge portion. Thatis, when a voltage lower than this lowest limit jetting voltage isapplied, jetting a droplet is not performed, but for example, bydefining a value higher than this lowest limit jetting voltage as aboarder as a jetting voltage, and by switching a voltage value lowerthan this and the jetting voltage, on-off control of the jettingoperation can be performed. In this case, the lower voltage value toswitch to the off state of the jetting is preferably close to the lowestlimit jetting voltage. Thereby, the voltage change width in the on-offswitch can be narrow, and thus, improving responsiveness.

Moreover, in addition to the above described structure, the nozzle maybe formed with a material having an insulating property, or at least theedge portion of the nozzle may be formed with a material having aninsulating property.

Here, the insulating property indicates dielectric breakdown strength ofnot less than 10[kV/mm], preferably not less than 21[kV/mm], and morepreferably not less than 30 [kV/mm]. The dielectric breakdown strengthindicates “strength for dielectric breakdown” described in JIS-C2110,and a value measured by a measuring method described in JIS-C2110.

By forming the nozzle in this way, discharge from the nozzle edgeportion can effectively be suppressed, and the liquid can be jetted inthe state where charging of electric charges of the liquid solution waseffectively performed, so that jetting can be smoothly and favorablyperformed.

Moreover, in addition to the above described structure, the nozzlediameter may be less than 20[μm].

Thereby, electric field intensity distribution becomes narrow.Therefore, the electric field can be concentrated. This results inmaking a droplet to be formed minute and stabilizing the shape thereof,and reducing the total applying voltage. The droplet just after jettedfrom the nozzle is accelerated by an electrostatic force acting betweenthe electric field and the charge. However, the electric field rapidlydecreases with the droplet moves away from the nozzle. Thus, thereafter,the droplet decreases the speed by air resistance. However, the minutedroplet with concentrated electric field is accelerated by an imageforce as it approaches the counter electrode. By balancing thedeceleration by air resistance and the acceleration by the image force,the minute droplet can stably fly and landing accuracy can be improved.

Moreover, the inside diameter of the nozzle may be not more than 10[μm].

Thereby, the electric field can further be concentrated, so that adroplet can further be made minute and the effect to the electric fieldintensity distribution by the distance change to the counter electrodewhen flying can be reduced. This results in reducing the effects to thedroplet shape or the landing accuracy by the positional accuracy of thecounter electrode or, the property or the thickness of the basematerial.

Moreover, the inside diameter of the nozzle may be not more than 8 [μm].

Thereby, the electric field can further be concentrated, so that adroplet can further be made minute and the effect to the electric fieldintensity distribution by the distance change to the counter electrodewhen flying can be reduced. This results in reducing the effects to thedroplet shape or the landing accuracy by the positional accuracy of thecounter electrode or, the property or the thickness of the basematerial.

Further, with the degree of the electric field concentration becomeshigh, the effect of electric field crosstalk which is a problem whenarranging nozzles in high density at the time of using a plurality ofnozzles is reduced, enabling to arrange the nozzles with further highdensity.

Moreover, the inside diameter of the nozzle may be not more than 4 [μm].With this structure, the electric field can significantly beconcentrated, thus, making maximum electric field intensity high, and adroplet can be super minute with a stable shape and the initial speed ofthe droplet can be increased. Thereby, flying stability improves,resulting in further improving the landing accuracy and jettingresponsiveness.

Further, with the degree of the electric field concentration becomeshigh, the effect of electric field crosstalk which is a problem whenarranging nozzles with high density at the time of using a plurality ofnozzles is reduced, enabling to arrange the nozzles with further highdensity.

Moreover, the inside diameter of the nozzle is preferably more than 0.2[μm]. By making the inside diameter of the nozzle be more than 0.2 [μm],charging efficiency of a droplet can be improved. Thus, jettingstability can be improved.

Further, in each above described structure, preferably the nozzle isformed with an electrical insulating material, and an electrode forapplying a jetting voltage is inserted in the nozzle or a plating tofunction as the electrode is formed.

Further, preferably the nozzle is formed with an electrical insulatingmaterial, an electrode for applying a jetting voltage is inserted in thenozzle or a plating to function as the electrode is formed, and anelectrode for jetting is also provided on the outside of the nozzle.

The electrode for jetting outside the nozzle is, for example, providedat the end surface of the edge portion side of the nozzle, or the entirecircumference or a part of the side surface of the edge portion side ofthe nozzle.

Further, in addition to the operational effects by the above describedstructures, a jetting force can be improved. Thus, a droplet can bejetted with low voltage even when further making the nozzle diameterminute.

Further, preferably, the base material is formed with a conductivematerial or an insulating material.

Further, preferably, the jetting voltage to be applied is not more than1000V.

By setting the upper limit of the jetting voltage in this way, jettingcontrol can be made easy and durability of the apparatus can be easilyimproved.

Further, preferably, the jetting voltage to be applied is not more than500V.

By setting the upper limit of the jetting voltage in this way, jettingcontrol can be further made easy and durability of the apparatus can beimproved more easily.

Further, preferably, a distance between the nozzle and the base materialis not more than 500 [μm], because high landing accuracy can be obtainedeven when making the nozzle diameter minute.

Further, preferably, the structure is such that a pressure is applied tothe liquid solution in the nozzle.

Further, when jetting is performed at a single pulse, a pulse width Δtnot less than a time constant I determined by the following equation (2)may be applied.

$\begin{matrix}{\tau = \frac{ɛ}{\sigma}} & (2)\end{matrix}$where, ε: dielectric constant of liquid solution [F/m], and σ:conductivity of liquid solution [S/m].

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view showing an electric field intensity distribution witha nozzle diameter as ø0.2 [μm] and with a distance from a nozzle to acounter electrode set to 2000 [μm], and FIG. 1B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 2A is a view showing an electric field intensity distribution withthe nozzle diameter as ø0.4 [μm] and with the distance from the nozzleto the counter electrode set to 2000 [μm], FIG. 2B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100[μm];

FIG. 3A is a view showing an electric field intensity distribution withthe nozzle diameter as ø1 [μm] and with a distance from the nozzle tothe counter electrode set to 2000[μm], FIG. 3B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 4A is a view showing an electric field intensity distribution withthe nozzle diameter as ø8 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 4B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 5A is a view showing an electric field intensity distribution withthe nozzle diameter as ø20 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 5B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 6A is a view showing an electric field intensity distribution withthe nozzle diameter as ø50 [μm] and with the distance from the nozzle tothe counter electrode set to 2000 [μm], FIG. 6B is a view showing anelectric field intensity distribution with the distance from the nozzleto the counter electrode set to 100 [μm];

FIG. 7 is a chart showing maximum electric field intensity under eachcondition of FIG. 1 to FIG. 6;

FIG. 8 is a diagram showing a relation between the nozzle diameter ofthe nozzle, and maximum electric field intensity and an intense electricfield area at a meniscus;

FIG. 9 is a diagram showing a relation among the nozzle diameter of thenozzle, a jetting start voltage at which a droplet jetted at themeniscus starts flying, a voltage value at Rayleigh limit of the initialjetted droplet, and a ratio of the jetting start voltage to the Rayleighlimit voltage;

FIG. 10 is a graph described by a relation between the nozzle diameterand the intense electric field area at the meniscus;

FIG. 11 is a sectional view along the nozzle of the liquid jettingapparatus in the first embodiment;

FIG. 12A is an explanation view of a relation between a jettingoperation of liquid solution and a voltage applied to the liquidsolution in a state where the jetting is not performed, FIG. 12B is anexplanation view showing the jetting state, and FIG. 12C is anexplanation view showing a state after the jetting;

FIG. 13 is a sectional view along the nozzle of the liquid jettingapparatus in the second embodiment;

FIG. 14A is an explanation view of a relation between the jettingoperation of liquid solution and a voltage applied to the liquidsolution in a state where the jetting is not performed, FIG. 14B is anexplanation view of a relation between the jetting operation of theliquid solution and the voltage applied to the liquid solution in thejetting state, and FIG. 14C is an explanation view of a relation betweenthe jetting operation of the liquid solution and the voltage applied tothe liquid solution after the jetting;

FIG. 15 is a sectional view along the nozzle showing an example in whicha heater is adopted to the liquid jetting apparatus;

FIG. 16A is an explanation view of a relation between the jettingoperation of the liquid solution and a voltage applied to the heater ina state where the jetting is not performed, FIG. 16B is an explanationview of a relation between the jetting operation of the liquid solutionand the voltage applied to the heater in the jetting state, and FIG. 16Cis an explanation view of a relation between the jetting operation ofthe liquid solution and the voltage applied to the heater after thejetting;

FIG. 17A is an explanation view of a relation between the jettingoperation of the liquid solution and the voltage applied to the liquidsolution in a state where the jetting is not performed, FIG. 17B is anexplanation view of a relation between the jetting operation of theliquid solution and the voltage applied to the liquid solution in thejetting state;

FIG. 18A is a partially broken perspective view showing an example of ashape of an in-nozzle passage providing roundness at a liquid solutionroom side, FIG. 18B is a partially broken perspective view showing anexample of a shape of the in-nozzle passage having an inside surfacethereof as a tapered circumferential surface, and FIG. 18C is apartially broken perspective view showing an example of a shape of thein-nozzle passage combining the tapered circumferential surface and alinear passage;

FIG. 19 is a chart showing comparative study results;

FIG. 20 is a view for describing a calculation of the electric fieldintensity of the nozzle of the embodiments of the present invention;

FIG. 21 is a side sectional view of the liquid jetting apparatus as oneexample of the present invention; and

FIG. 22 is a view for describing a jetting condition according to arelation of distance-voltage in the liquid jetting apparatus of theembodiments of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A nozzle diameter of a liquid jetting apparatus described in thefollowing each embodiment is preferably not more than 30 [μm], morepreferably less than 20 [μm], even more preferably not more than 10[μm], even more preferably not more than 8 [μm], and even morepreferably not more than 4 [μm]. Also, the nozzle diameter is preferablymore than 0.2 [μm]. Hereinafter, in regard to a relation between thenozzle diameter and an electric field intensity, descriptions will behereafter made with reference to FIG. 1A to FIG. 6B. In correspondencewith FIG. 1A to FIG. 6B, electric field intensity distributions in casesof the nozzle diameters being ø0.2, 0.4, 1, 8 and 20 [μm], and a case ofa conventionally-used nozzle diameter being ø50 [μm] as a reference areshown.

Here, in FIG. 1A to FIG. 6B, a nozzle center position C indicates acenter position of a liquid jetting surface of a liquid jetting hole ata nozzle edge. Further, FIG. 1A, FIG. 2A, FIG. 3A, FIG. 4A, FIG. 5A, andFIG. 6A indicate electric field intensity distributions when thedistance between the nozzle and an counter electrode is set to 2000[μm], and FIG. 1B, FIG. 2B, FIG. 3B, FIG. 4B, FIG. 5B, and FIG. 6Bindicate electric field intensity distributions when the distancebetween the nozzle and the counter electrode is set to 100 [μm]. Here,an applying voltage is set constant to 200 [V] in each condition. Adistribution line in FIG. 1A to FIG. 6B indicates a range of electriccharge intensity from 1×10⁶ [V/m] to 1×10⁷ [V/m].

FIG. 7 shows a chart indicating maximum electric field intensity undereach condition.

According to FIG. 5A and FIG. 5B, the fact that the electric fieldintensity distribution spreads to a large area if the nozzle diameter isnot less than ø20 [μm], was comprehended. Further, according to thechart of FIG. 7, the fact that the distance between the nozzle and thecounter electrode has an influence on the electric field intensity wascomprehended.

From these things, when the nozzle diameter is not more than ø8 [μm](see FIG. 4A and FIG. 4B), the electric field intensity is concentratedand change of a distance to the counter electrode scarcely has aninfluence on the electric field intensity distribution. Therefore, whenthe nozzle diameter is not more than ø8 [μm], it is possible to performa stable jetting without suffering influence of position accuracy of thecounter electrode, and unevenness of base material property andthickness. Next, a relation between the nozzle diameter of the nozzleand the maximum electric field intensity and an intense electric fieldarea when a liquid level is at the edge position of the nozzle is shownin FIG. 8.

According to the graph shown in FIG. 8, when the nozzle diameter is notmore than ø4 [μm], the fact that the electric field concentration growsextremely large and the maximum electric field intensity is made highwas comprehended. Thereby, since it is possible to make an initialjetting speed of the liquid solution large, flying stability of adroplet is increased and a moving speed of an electric charge at thenozzle edge portion is increased, thereby jetting responsivenessimproves.

Continuously, in regard to maximum electric charge amount chargeable toa jetted droplet, description will be made hereafter. Electric chargeamount chargeable to a droplet is shown as the following equation (3),in consideration of Rayleigh fission (Rayleigh limit) of a droplet.

$\begin{matrix}{q = {8 \times \pi \times \sqrt{ɛ_{0} \times \gamma \times \frac{d_{0}^{3}}{8}}}} & (3)\end{matrix}$where, q is electric charge amount [C] giving Rayleigh limit, ε₀ iselectric constant [F/m], γ is surface tension of the liquid solution[N/m], and d₀ is diameter [m] of the droplet.

The closer to a Rayleigh limit value the electric charge amount qcalculated by the above-mentioned equation (3) is, the stronger anelectrostatic force becomes even with the same electric field intensity,thereby improving jetting stability. However, when it is too close tothe Rayleigh limit value, conversely a dispersion of the liquid solutionoccurs at a liquid jet opening of the nozzle, and there is lack ofjetting stability.

Here, FIG. 9 is a graph showing a relation among the nozzle diameter ofthe nozzle, a jetting start voltage at which a droplet jetted at thenozzle edge portion starts flying, a voltage value at Rayleigh limit ofthe initial jetted droplet, and a ratio of the jetting start voltage tothe Rayleigh limit voltage.

From the graph shown in FIG. 9, within the range of the nozzle diameterfrom ø0.2 [μm] to ø4 [μm], the ratio of the jetting start voltage andthe Rayleigh limit voltage value exceeds 0.6, and a favorable result ofelectric charge efficiency of a droplet is obtained. Thereby, it iscomprehended that it is possible to perform a stable jetting within therange.

For example, in a graph represented by a relation between a nozzlediameter and an intense electric field (not less than 1×10⁶ [V/m]) areaat the nozzle edge portion shown in FIG. 10, the fact that an area ofthe electric field concentration becomes extremely narrow when thenozzle diameter is not more than ø0.2 [μm] is indicated. Thereby, thefact that a jetted droplet is not able to sufficiently receive energyfor acceleration and flying stability is reduced is indicated.Therefore, preferably the nozzle diameter is set to more than ø0.2 [μm].

First Embodiment

(Whole Structure of Liquid Jetting Apparatus)

A liquid jetting apparatus 20 as the first embodiment of the presentinvention will be described below with reference to FIG. 11 to FIGS. 12.FIG. 11 is a sectional view along a nozzle 21 to be described later ofthe liquid jetting apparatus 20, and FIGS. 12 are explanation views of arelation between a jetting operation of the liquid solution and avoltage applied to the liquid solution, wherein FIG. 12A shows a statewhere the jetting is not performed, FIG. 12B shows a state where thejetting is performed, and FIG. 12C shows a state after the jetting.

The liquid jetting apparatus 20 comprises the nozzle 21 having a superminute diameter for jetting a droplet of chargeable liquid solution fromits edge portion, a counter electrode 23 which has a facing surface toface the edge portion of the nozzle 21 and supports a base material Kreceiving a droplet at the facing surface, a liquid solution supplyingsection 29 for supplying the liquid solution to a passage 22 in thenozzle 21, a jetting voltage applying section 25 for applying a jettingvoltage to the liquid solution in the nozzle 21, a convex meniscusforming section 40 for forming a state where the liquid solution in thenozzle 21 protrudes to be a convex shape from the edge portion of thenozzle 21, and an operation control section 50 for controlling applyinga driving voltage of the convex meniscus forming section 40 and ajetting voltage by the jetting voltage applying section 25. Theabove-mentioned nozzle 21, a partial structure of the liquid solutionsupplying section and a partial structure of the jetting voltageapplying section 25 are integrally formed as a liquid jetting head.

In FIG. 11, for the convenience of a description, a state where the edgeportion of the nozzle 21 faces upward and the counter electrode 23 isprovided above the nozzle 21 is illustrated. However, practically, theapparatus is so used that the nozzle 21 faces in a horizontal directionor a lower direction than the horizontal direction, more preferably, thenozzle 21 faces perpendicularly downward.

(Liquid Solution)

As an example of the liquid solution jetted by the above-mentionedliquid jetting apparatus 20, as inorganic liquid, water, COCl₂, HBr,HNO₃, H₃PO₄, H₂SO₄, SOCl₂, SO₂CL₂, FSO₂H and the like can be cited. Asorganic liquid, alcohols such as methanol, n-propanol, isopropanol,n-butanol, 2-methyl-1-propanol, tert-butanol, 4-metyl-2-pentanol, benzylalcohol, α-terpineol, ethylene glycol, glycerin, diethylene glycol,triethylene glycol and the like; phenols such as phenol, o-cresol,m-cresol, p-cresol and the like; ethers such as dioxiane, furfural,ethyleneglycoldimethylether, methylcellosolve, ethylcellosolve,butylcellosolve, ethylcarbitol, buthylcarbito, buthylcarbitolacetate,epichlorohydrin and the like; ketones such as acetone, ethyl methylketone, 2-methyl-4-pentanone, acetophenone and the like; aliphatic acidssuch as formic acid, acetic acid, dichloroacetate, trichloroacetate andthe like; esters such as methyl formate, ethyl formate, methyl acetate,ethyl acetate, n-butyl acetate, isobutyl acetate, 3-methoxybutylacetate, n-pentyl acetate, ethyl propionate, ethyl lactate, methylbenzonate, diethyl malonate, dimethyl phthalate, diethyl phthalate,diethyl carbonate, ethylene carbonate, propylene carbonate, cellosolveacetate, butylcarbitol acetate, ethyl acetoacetate, methyl cyanoacetate,ethyl cyanoacetate and the like; nitrogen-containing compounds such asnitromethane, nitrobenzene, acetonitrile, propionitrile, succinonitrile,valeronitrile, benzonitrile, ethyl amine, diethyl amine,ethylenediamine, aniline, N-methylaniline, N,N-dimethylaniline,o-toluidine, p-toluidine, piperidine, pyridine, α-picoline,2,6-lutidine, quinoline, propylene diamine, formamide,N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide,acetamide, N-methylacetamide, N-methylpropionamide,N,N,N′,N′-tetramethylurea, N-methylpyrrolidone and the like;sulfur-containing compounds such as dimethyl sulfoxide, sulfolane andthe like; hydro carbons such as benzene, p-cymene, naphthalene,cyclohexylbenzene, cyclohexyene and the like; halogenated hydrocarbonssuch as 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane,1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane,1,2-dichloroethylene(cis-), tetrachloroethylene, 2-chlorobutan,1-chloro-2-methylpropane, 2-chloro-2-methylpropane, bromomethane,tribromomethane, 1-promopropane and the like can be cited. Further, twoor more types of each of the mentioned liquids may be mixed to be usedas the liquid solution.

Further, conductive paste which includes large portion of materialhaving high electric conductivity (silver pigment or the like) is used,and in the case of performing the jetting, as objective material forbeing dissolved into or dispersed into the above-mentioned liquid,excluding coarse particles causing clogging to the nozzles, it is not inparticular limited. As fluorescent material such as PDP, CRT, FED or thelike, what is conventionally known can be used without any specificlimitation. For example, as red fluorescent material, (Y,Gd)BO₃:Eu,YO₃:Eu and the like, as red fluorescent material, Zn₂SiO₄:Mn,BaAl₁₂O₁₉:Mn, (Ba,Sr,Mg)O.α-Al₂O₃:Mn and the like, blue fluorescentmaterial, BaMgAl₁₄O₂₃:Eu, BaMgAl₁₀O₁₇:Eu and the like can be cited. Inorder to make the above-mentioned objective material adhere on arecording medium firmly, it is preferably to add various types ofbinders. As a binder to be used, for example, cellulose and itsderivative such as ethyl cellulose, methyl cellulose, nitrocellulose,cellulose acetate, hydroxyethyl cellulose and the like; alkyd resin;(metha)acrylate resin and its metal salt such as polymethacrytacrylate,polymethylmethacrylate, 2-ethylhexylmethacrylate methacrylic acidcopolymer, lauryl methacrylate•2-hydroxyethylmethacrylate copolymer andthe like; poly(metha)acrylamide resin such aspoly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide and the like;styrene resins such as polystyrene, acrylonitrile•styrene copolymer,styrene.maleate copolymer, styrene•isoprene copolymer and the like;various saturated or unsaturated polyester resins; polyolefin resinssuch as polypropylene and the like; halogenated polymers such aspolyvinyl chloride, polyvinylidene chloride and the like; vinyl resinssuch as poly vinyl acetate, chloroethene•polyvinyl acetate copolymer andthe like; polycarbonate resin; epoxy resins; polyurethane resins;polyacetal resins such as polyvinyl formal, polyvinyl butyral, polyvinylacetal and the like; polyethylene resins such as ethylene•vinyl acetatecopolymer, ethylene•ethyl acrylate copolymer resin and the like; amideresins such as benzoguanamine and the like; urea resin; melamine resin;polyvinyl alcohol resin and its anion cation degeneration; polyvinylpyrrolidone and its copolymer; alkylene oxide homopolymer, copolymer andcross-linkage such as polyethelene oxide, polyethelene oxide carboxylateand the like; polyalkylene glycol such as polyethylene glycol,polypropylene glycol and the like; poryether polyol; SBR, NBR latex;dextrin; sodium alginate; natural or semisynthetic resins such asgelatin and its derivative, casein, Hibiscus manihot, gum traganth,pullulan, gum arabic, locust bean gum, guar gum, pectin, carrageenan,glue, albumin, various types of starches, corn starch, arum root,funori, agar, soybean protein and the like; terpene resin; ketone resin;rosin and rosin ester; polyvinylmethylether, polyethyleneimine,polystyrene sulfonate, polyvinyl sulfonate and the like can be used.These resins may not only be used as homopolymer but be blended within amutually soluble range to be used.

When the liquid jetting apparatus 20 is used as a patterning method, asa representative example, it is possible to use it for display use.Concretely, it is possible to cite formation of fluorescent material ofplasma display, formation of rib of plasma display, formation ofelectrode of plasma display, formation of fluorescent material of CRT,formation of fluorescent material of FED (Field Emission type Display),formation of rib of FED, color filter for liquid crystal display (RGBcoloring layer, black matrix layer), spacer for liquid crystal display(pattern corresponding to black matrix, dot pattern and the like). Therib mentioned here means a barrier in general, and with plasma displaytaken as an example, it is used for separating plasma areas of eachcolor. For other uses, it is possible to apply it to microlens,patterning coating of magnetic material, ferrodielectric substance,conductive paste (wire, antenna) and the like for semiconductor use, asgraphic use, normal printing, printing to special medium (film, fabric,steel plate), curved surface printing, lithographic plate of variousprinting plates, for processing use, coating of adhesive, sealer and thelike using the present embodiment, for biotechnological, medical use,pharmaceuticals (such as one mixing a plurality of small amount ofcomponents), coating of sample for gene diagnosis or the like.

(Nozzle)

The above nozzle 21 is integrally formed with a nozzle plate 26 c to bedescribed later, and is provided to stand up perpendicularly withrespect to a flat plate surface of the nozzle plate 26 c. Further, atthe time of jetting a droplet, the nozzle 21 is used to perpendicularlyface a receiving surface (surface where the droplet lands) of the basematerial K. Further, in the nozzle 21, the in-nozzle passage 22penetrating from its edge portion along the nozzle center is formed.

The nozzle 21 will be described in more detail. In the nozzle 21, anopening diameter of its edge portion and the in-nozzle passage 22 areuniform, and as mentioned, these are formed as a super minute diameter.As one concrete example of dimensions of each part, an inside diameterof the in-nozzle passage 22 is preferably not more than 30 [μm], morepreferably less than 20 [μm], even more preferably not more than 10[μm], even more preferably not more than 8 [μm], and even morepreferably not more than 4 [μm], and in this embodiment, the insidediameter of the in-nozzle passage 22 is set to 1 [μm]. An outsidediameter of the edge portion of the nozzle 21 is set to 2 [μm], adiameter of the root of the nozzle 21 is 5 [μm], and a height of thenozzle 21 is set to 100 [μm], and its shape is formed as a truncatedconic shape being unlimitedly close to a conic shape. The insidediameter of the nozzle is preferably more than 0.2 [μm]. The height ofthe nozzle 21 may be 0 [μm].

In addition, a shape of the in-nozzle passage 22 may not be formedlinearly with the inside diameter constant as shown in FIG. 11. Forexample, as shown in FIG. 18A, it may be so formed as to give roundnessto a cross-section shape at the edge portion of the side of a liquidsolution room 24 to be described later, of the in-nozzle passage 22.Further, as shown in FIG. 18B, an inside diameter at the end portion ofthe side of the liquid solution room 24 to be described later, of thein-nozzle passage 22 may be set to be larger than an inside diameter ofthe end portion at the jetting side, and an inside surface of thein-nozzle passage 22 may be formed in a tapered circumferential surfaceshape. Further, as shown in FIG. 18C, only the end portion of the sideat the liquid solution room 24 to be describe later, of the in-nozzlepassage 22 may be formed in a tapered circumferential surface shape andthe jetting end portion side with respect to the tapered circumferentialsurface may be formed linearly with the inside diameter constant.

(Liquid Solution Supplying Section)

The liquid solution supplying section 29 is provided at a position beinginside of the liquid jetting head 26 and at the root of the nozzle 21,and comprises the liquid solution room 24 communicated to the in-nozzlepassage 22, a supplying passage 27 for guiding the liquid solution froman external liquid solution tank which is not shown, to the liquidsolution room 24, and a not shown supplying pump for giving a supplyingpressure of the liquid solution to the liquid solution room 24.

The above-mentioned supplying pump supplies the liquid solution to theedge portion of the nozzle 21, and supplies the liquid solution whilemaintaining the supplying pressure within a not-dripping range (refer toFIG. 12A).

The supplying pump includes the case of using a pressure differenceaccording to arrangement positions of the liquid jetting head and thesupplying tank, and may be formed only with a liquid supplying passagewithout separately providing the liquid solution section. Although itdepends upon the design of the pump system, basically, the supplyingpump operates when supplying the liquid solution to the liquid jettinghead at the start time, jetting the liquid from the liquid jetting head56, and supplying of the liquid solution according thereto is performedwhile optimizing capacity change in the liquid jetting head by acapillary and the convex meniscus forming section and each pressure ofthe supplying pumps.

(Jetting Voltage Applying Section)

The jetting voltage applying section 25 comprises a jetting electrode 28for applying a jetting voltage, the jetting electrode 28 being providedinside the liquid jetting head 26 and at a border position between theliquid solution room 24 and the in-nozzle passage 22, and a directcurrent power source 30 for always applying a direct current jettingvoltage to this jetting electrode 28.

The above-mentioned jetting electrode 28 directly contacts the liquidsolution in the liquid solution room 24, for charging the liquidsolution and applying the jetting voltage.

In regard to the jetting voltage by the direct current power source 30,the direct current power source 30 is controlled by the operationcontrol section 50 so that a voltage value is in the range that adroplet can first be jetted in a state where convex meniscus by theliquid solution has already been formed at the edge portion of thenozzle 21, and a droplet can not be jetted in a state where the convexmeniscus has not been formed.

The jetting voltage applied by the direct current power source 30 istheoretically calculated by the following equation (1).

$\begin{matrix}{{h\sqrt{\frac{\gamma\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2\; ɛ_{0}}}} & (1)\end{matrix}$where, γ: surface tension of liquid solution [N/m], ε₀: electricconstant [F/m], d: nozzle diameter. [m], h: distance between nozzle andbase material [m], k: proportionality constant dependent on nozzle shape(1.5<k<8.5).

The above conditions are theoretical values, thus, practically,experiments may be performed at the time when the convex meniscus isformed and not formed to calculate appropriate voltage values.

In the embodiment, the jetting voltage is set to 400[V] as an example.

(Liquid Jetting Head)

The liquid jetting head 26 comprises a flexible base layer 26 a which ismade of material with flexibility (for example, metal, silicon, resin orthe like) and is placed at the lowest layer in FIG. 11, an insulatinglayer 26 d which is made of insulating material and is formed on theentire upper surface of the flexible base layer 26 a, a passage layer 26b which is placed on top thereof and forms a supplying passage of theliquid solution, and a nozzle plate 26 c formed further on top of thispassage layer 26 b. The above-mentioned jetting electrode 28 is insertedbetween the passage layer 26 b and the nozzle plate 26 c.

The flexible base layer 26 a may be, as described above, formed frommaterial with flexibility, and a metal thin plate may be used as oneexample. Flexibility is required because the flexible base layer 26 a isdeformed when a piezo element 41 of the convex meniscus forming section40 to be described later is provided at the position on the outersurface of the flexible base layer 26 a corresponding to the liquidsolution room 24. That is, by applying a predetermined voltage to thepiezo element 41 and making the flexible base layer 26 a dent in eitherinside or outside at the above position, internal capacity of the liquidsolution room 24 is decreased or increased, thereby, according to achange of the internal pressure, it is possible to form the convexmeniscus of the liquid solution at the edge portion of the nozzle 21 ordraw the liquid level to the inside.

A resin film with high insulating properties is formed on the uppersurface of the flexible base layer 26 a to form an insulating layer 26d. The insulating layer 26 d is formed thin enough not to prevent theflexible base layer 26 a from denting, or is made of resin materialwhich is deformed more easily.

A soluble resin layer is formed on the insulating layer 26 d, which iseliminated only leaving a portion corresponding to the predeterminedpattern for forming the supplying passage 27 and the liquid solutionroom 24, and an insulating resin layer is formed on a portion from whichthe resin layer is eliminated excluding the remaining portion. Thisinsulating resin layer functions as the passage layer 26 b. Then, thejetting electrode 28 is flatly formed on an upper surface of thisinsulating resin layer with plating of a conductive element (for exampleNiP), and a resist resin layer or parylene layer having insulatingproperties is formed further on top thereof. Since this resist resinlayer becomes the nozzle plate 26 c, this resin layer is formed withthickness in consideration of a height of the nozzle 21. Then, thisinsulating resist resin layer is exposed by an electron beam method orfemtosecond laser, for forming a nozzle shape. The in-nozzle passage 22is also formed by a laser processing. Then, the soluble resin layercorresponding to the pattern of the supplying passage 27 and the liquidsolution room 24 is eliminated, these supplying passage 27 and theliquid solution room 24 are communicated, and the production of theliquid jetting head 26 is completed.

In addition, material of the nozzle plate 26 c and the nozzle 21 may be,concretely, semiconductor such as Si or the like, conductive materialsuch as Ni, SUS or the like, other than insulating material such asepoxy, PMMA, phenol, soda glass. However, in a case of forming thenozzle plate 26 c and the nozzle 21 from conductive material, at leastat the edge portion edge surface of the edge portion of the nozzle 21,more preferably at the circumferential surface of the edge portion,coating by insulating material is preferably provided. This is because,by forming the nozzle 21 from insulating material or forming theinsulating material coating at its edge portion surface, at the time ofapplying the jetting voltage to the liquid solution, it is possible toeffectively suppress leakage of electric current from the nozzle edgeportion to the counter electrode 23.

(Counter Electrode)

The counter electrode 23 comprises a facing surface perpendicular to aprotruding direction of the nozzle 21, and supports the base material Kalong the facing surface. A distance from the edge portion of the nozzle21 to the facing surface of the counter electrode 23 is, as one example,set to 100 [μm], preferably not more than 500 [μm], and more preferablynot more than 100 [μm].

Further, since this counter electrode 23 is grounded, the counterelectrode 23 always maintains grounded potential. Therefore, a dropletjetted by an electrostatic force by electric field generated between theedge portion of the nozzle 21 and the facing surface is guided to a sideof the counter electrode 23.

In addition, since the liquid jetting apparatus 20 jets a droplet byenhancing the electric field intensity by the electric fieldconcentration at the edge portion of the nozzle 21 according tosuper-miniaturization of the nozzle 21, it is possible to jet thedroplet without the guiding by the counter electrode 23. However, theguiding by an electrostatic force between the nozzle 21 and the counterelectrode 23 is preferably performed. Further, it is possible to let outthe electric charge of a charged droplet by grounding the counterelectrode 23.

(Convex Meniscus Forming Section)

The convex meniscus section 40 comprises the piezo element 41 as apiezoelectric element arranged on the position corresponding to theliquid solution room 24 at the outer side surface of the flexible baselayer 26 a of the nozzle plate 26 (lower surface in FIG. 11), and adriving voltage power source 42 for applying a driving pulse voltage forchanging a shape of this piezo element 41.

The above piezo element 41 is attached to the flexible base layer 26 aso that the flexible base layer 26 a is deformed in a direction to dentin any of the inside or outside.

The driving voltage power source 42 outputs the driving pulse voltage(for example, 10 [V]) corresponding to a first voltage value appropriatefor the piezo element 41 to appropriately reduce the capacity of theliquid solution room 24 to transfer to the state where the liquidsolution in the in-nozzle passage 22 forms the convex meniscus at theedge portion of the nozzle 21 (refer to FIG. 12B) from the state where aconcave meniscus is formed (refer to FIG. 12A) by the control of theoperation control section 50. Further, the driving voltage power source42 outputs the driving pulse voltage corresponding to a second voltagevalue appropriate for the piezo element 41 to appropriately increase thecapacity of the liquid solution room 24 to transfer from the state wherethe liquid solution in the in-nozzle passage 22 forms the concavemeniscus at the edge portion of the nozzle 21 (refer to FIG. 12A) to thestate where the liquid level is drawn into a predetermined distance(refer to FIG. 12C) by the control of the operation control section 50.The driving pulse voltage of the second voltage value needs to deformthe piezo element 41 in a direction opposite to the deforming directionof the piezo element 41 by applying the driving pulse voltage of thefirst voltage value, so that the second voltage value has a reversepolarity of the first voltage value. The drawing distance of the liquidlevel is not specially limited, however, it may be a degree that theliquid level stops at a position in the middle of the in-nozzle passage22.

As another driving pattern, the first voltage value has been alwaysapplied in the state where the concave meniscus of the liquid solutionis formed at the edge portion of the nozzle 21 in the in-nozzle passage22 (refer to FIG. 12A), and the liquid solution 24 is in the reducedstate. Next, for transferring to the state to form the convex meniscus(refer to FIG. 12B), further, the driving pulse voltage corresponding tothe second voltage value appropriate for the piezo element 41 toappropriately reduce the liquid solution in the liquid solution room 24is output. The driving voltage power source 42 can set a voltage to 0[V] for the piezo element 41 to appropriately increase the capacity ofthe liquid solution room 24 to transfer from the state where the liquidsolution in the in-nozzle passage 22 forms the concave meniscus at theedge portion of the nozzle 21 (refer to FIG. 12A) to the state where theliquid level is drawn into a predetermined distance (refer to FIG. 12C)by the control of the operation control section 50.

(Operation Control Section)

The operation control section 50 is in practice structured from acalculation device including a CPU, a ROM, a RAM and the like, to whicha predetermined program is input to thereby realize the followingfunctional structure and perform the following operation control.

The above operation control section 50 makes the direct current powersource 30 apply the jetting voltage continuously, and comprises a firstjetting control unit 51 for controlling the application of the drivingpulse voltage of the first voltage value by the driving voltage powersource 42 when receiving the input of a jetting instruction fromoutside, and a liquid level stabilization control unit 52 for performingan operation control to make the driving pulse voltage of the secondvoltage value applied by the driving voltage power source 42 after theapplication of the driving pulse voltage of the first voltage value.

The operation control section 50 comprises a not shown receiving sectionto receive the jetting instruction signal from outside.

The first jetting control unit 51 makes the direct current power source30 apply the jetting voltage to be always constant to the jettingelectrode 28. Further, the first jetting control unit 51 recognizes thereception of the jetting instruction signal through the receivingsection to make the driving voltage power source 42 apply the drivingpulse voltage of the first voltage value to the piezo element 41.Thereby, jetting a droplet from the edge portion of the nozzle 21 isperformed.

The liquid level stabilization control unit 52 recognizes the output ofthe driving pulse voltage of the first voltage value of the drivingvoltage power source 42 by the first jetting control unit 51, andimmediately thereafter, makes the driving voltage power source 42 applythe driving pulse voltage of the second voltage value to the piezoelement 41.

(Jetting Operation of Minute Droplet by Liquid Jetting)

An operation of the liquid jetting apparatus 20 will be described withreference to FIG. 11 to FIG. 12C.

The state is such that the liquid solution has been supplied to thein-nozzle passage 22 by the supplying pump of the liquid solutionsupplying section, and in this state, the jetting voltage is applied tobe always constant to the jetting electrode 28 from the direct currentpower source 30 (FIG. 12A). In this state, the liquid solution is in acharged state.

Then, when a jetting instruction signal is input to the operationcontrol section 50 from outside, according to the control of the firstjetting control unit 51, the driving pulse voltage of the first voltagevalue by the driving voltage power source 42 is applied to the piezoelement 41. Thereby, the electric field intensity is made high due tothe electric field concentration state by the charged liquid solutionand convex meniscus forming state at the edge portion of the nozzle 21,and a minute droplet is jetted at the top of the convex meniscus (FIG.12B).

After jetting the droplet, although the convex meniscus becomes avibration state, the driving pulse voltage of the second voltage valueby the driving voltage power source 42 is applied to the piezo element41 by the liquid level stabilization control unit 52 immediately, sothat the convex meniscus disappears, and the liquid level of the liquidsolution is drawn to the inside of the nozzle 21 (FIG. 12C). Thedisappearance of the convex meniscus and the movement of the liquidsolution in the nozzle 21 of low conductance due to the minute diameterstop the vibration state. The drawn state of the liquid level at theedge portion of the nozzle 21 is temporary because of the pulse voltage,and can back to the state of FIG. 12A.

As described above, a constant voltage is always applied to the liquidsolution by the first jetting control unit 51 irrespective of performingor not performing the jetting, so that improvement of responsiveness atjetting and stabilization of liquid volume can be achieved.

The liquid level stabilization control unit can suppress vibration bythe convex meniscus forming section just after jetting by sucking, sothat next jetting can be performed without waiting a lapse of waitingtime for the convex meniscus to stop the vibration, enabling to easilydeal with continuous jetting operations.

Further, since the above-mentioned liquid jetting apparatus 20 jets adroplet by the nozzle 21 having minute diameter which cannot be foundconventionally, the electric field is concentrated by the liquidsolution in a charged state in the in-nozzle passage 22, and thereby theelectric field intensity is enhanced. Therefore, jetting of the liquidsolution by a nozzle having a minute diameter (for example, an insidediameter of 100 [μm]), which was conventionally regarded assubstantially impossible since a voltage necessary for jetting wouldbecome too high with a nozzle having a structure in which concentrationof the electric field is not performed, is now possible with a lowervoltage than the conventional one.

Since liquid solution flow at the in-nozzle passage 22 is restrictedbecause of low conductance due to the minute nozzle diameter, it ispossible to do the control to easily reduce jetting quantity per unittime, and the jetting of the liquid solution with a sufficiently-smalldroplet diameter (0.8 [μm] according to each above-mentioned condition)without narrowing a pulse width is realized.

Further, since the jetted droplet is charged, even though it is a minutedroplet, a vapor pressure is reduced and evaporation is suppressed, andthereby the loss of mass of the droplet is reduced, the flyingstabilization is achieved and the decrease of landing accuracy of thedroplet is prevented.

In addition, for obtaining electro wetting effect to the nozzle 21, anelectrode may be provided at a circumference of the nozzle 21, or anelectrode may be provided at an inside surface of the in-nozzle passage22 and an insulating film may cover over it. Then, by applying a voltageto this electrode, it is possible to enhance wettability of the insidesurface of the in-nozzle passage 22 with respect to the liquid solutionto which the voltage is applied by the jetting electrode 28 according tothe electro wetting effect, and thereby it is possible to smoothlysupply the liquid solution to the in-nozzle passage 22, resulting inpreferably performing the jetting and improving responsiveness of thejetting.

Further, the jetting voltage applying section 25 always applies the biasvoltage and jets a droplet by using the pulse voltage as a trigger.However, it may be possible to have a structure where jetting isperformed by always applying alternate current with amplitude necessaryfor jetting or continuous rectangular wave and by changing high and lowof its frequency. It is essential to have the liquid solution chargedfor jetting a droplet, and when the jetting voltage is applied at afrequency exceeding a speed at which the liquid solution is charged, thejetting is not performed, but the jetting is performed when it isswitched to a frequency at which it is possible to charge the liquidsolution sufficiently. Therefore, by doing the control to apply thejetting voltage with a frequency larger than a frequency at which it ispossible to jet when jetting is not performed, and to reduce thefrequency to a frequency band where it is possible to perform thejetting only when the jetting is to be performed, it is possible tocontrol the jetting of the liquid solution. In such a case, since anelectric potential to be applied to the liquid solution does not have achange in itself, it is possible to improve time responsiveness evenmore, and thereby it is possible to improve landing accuracy of adroplet.

Second Embodiment

Next, a liquid jetting apparatus 20A as the second embodiment of thepresent invention will be explained based on FIG. 13 to FIG. 14C. FIG.13 is a sectional view of the liquid jetting apparatus 20A, and FIG.14A, FIG. 14B, and FIG. 14C are explanation views of a relation betweena jetting operation of liquid solution and a voltage applied to theliquid solution. FIG. 14A shows a state where the jetting is notperformed, FIG. 14B shows a jetting state, and FIG. 14C shows a stateafter the jetting. In FIG. 13, for the convenience of a description, astate where the edge portion of the nozzle 21 faces upward isillustrated. However, practically, the apparatus is so used that thenozzle 21 faces in a horizontal direction or a lower direction than thehorizontal direction, more preferably, the nozzle 21 facesperpendicularly downward.

In the explanation of the embodiment, the component that is same as thatof the liquid jetting apparatus 20 in the first embodiment will be giventhe same reference numeral, thus the overlapping explanations areomitted here.

(Whole Structure of Liquid Jetting Apparatus)

The features of the liquid jetting apparatus 20A in comparison to theabove described liquid jetting apparatus 20 are a jetting voltageapplying section 25A for applying a jetting voltage to the liquidsolution in the nozzle 21, and an operation control section 50A forcontrolling applying a driving voltage of the convex meniscus formingsection 40 and the jetting voltage by the jetting voltage applyingsection 25A. Thus, only the explanations thereof will be made.

(Jetting Voltage Applying Section)

The jetting voltage applying section 25A comprises the above describedjetting electrode 28 for applying the jetting voltage, a bias powersource 30A for always applying a direct current bias voltage to thisjetting electrode 28, and a jetting voltage power source 31A forapplying a jetting pulse voltage to the jetting electrode 28 with thebias voltage superimposed to be an electric potential for jetting.

In regard to the bias voltage by the bias power source 30A, by alwaysapplying a voltage within a range within which jetting of the liquidsolution is not performed, width of a voltage to be applied at jettingis preliminarily reduced, herewith responsiveness at jetting isimproved.

The jetting voltage power source 31A is controlled by the operationcontrol section 50A so that a voltage value is in the range where adroplet can first be jetted in a state where convex meniscus by theliquid solution has already been formed at the edge portion of thenozzle 21, and a droplet can not be jetted in a state where the convexmeniscus has not been formed, in the case of superimposing the biasvoltage.

The jetting pulse voltage applied by the jetting voltage power source31A is calculated by the above described equation (1) in a state ofbeing superimposed on the bias voltage.

The above conditions are theoretical values, thus, practically,experiments may be performed at the time when the convex meniscus isformed and not formed to calculate appropriate voltage values. As oneexample, the bias voltage is applied at DC300 [V], and the jetting pulsevoltage is applied at 100 [V]. Therefore, the superimposed voltage atjetting is 400 [V].

(Operation Control Section)

The operation control section 50A practically is structured by acalculation device including a CPU, a ROM, a RAM and the like, to whicha predetermined program is input to thereby realize the followingfunctional structure and perform the following operation control.

The above operation control section 50A comprises a second jettingcontrol unit 51A for controlling the applications of the jetting pulsevoltage by the jetting voltage power source 31A and the driving pulsevoltage of the first voltage value by the driving voltage power source42 in synchronization with each other when receiving the input of ajetting instruction from outside in a state of continuously making thebias power source 30A apply the bias voltage, and the liquid levelstabilization control unit 52 for performing the operation control tomake the driving voltage power source 42 apply the driving pulse voltageof the second voltage value after the application of the jetting pulsevoltage and the driving pulse voltage of the first voltage value.

The operation control section 50A comprises a not shown receivingsection to receive a jetting instruction signal from outside.

The second jetting control unit 51A makes the bias power source 30Aapply the bias voltage to be always constant to the jetting electrode28. Further, the second jetting control unit 51A recognizes reception ofthe jetting instruction signal via the receiving section to make thejetting voltage power source 31A apply the jetting pulse voltage andmake the driving voltage power source 42 apply the driving pulse voltageof the first voltage value in synchronization with each other. Thereby,jetting of a droplet from the edge portion of the nozzle 21 isperformed.

Here, the synchronization described above includes both cases of makingthe voltages applied exactly at the same time, and making the voltagesapplied approximately at the same time after considering responsivenessby charging speed of the liquid solution and responsiveness by pressurechange by the piezo element 41 and adjusting the difference betweenthem.

(Jetting Operation of Minute Droplet by Liquid Jetting Apparatus)

An operation of the liquid jetting apparatus 20A will be described withreference to FIG. 13 and FIG. 14C.

The state is such that the liquid solution has been supplied to thein-nozzle passage 22 by the supplying pump of a liquid solutionsupplying section, and in this state, the bias voltage is applied to bealways constant to the jetting electrode 28 from the bias power source30A (FIG. 14A).

Then, when a jetting instruction signal is input to the operationcontrol section 50A from outside, according to the control of the secondjetting control unit 51A, application of the jetting pulse voltage tothe jetting electrode 28 by the jetting voltage power source 31A andapplication of the driving pulse voltage of the first voltage value tothe piezo element 41 by the driving voltage power source 42 areperformed in synchronization with each other. Thereby, the electricfield intensity are made high due to the electric field concentrationstate by the charged liquid solution and convex meniscus forming stateby the edge portion of the nozzle 21, thereby jetting a minute dropletat the top of the convex meniscus (FIG. 14B).

After jetting the droplet, although the convex meniscus becomes avibration state, the driving pulse voltage of the second voltage valueby the driving voltage power source 42 is applied to the piezo element41 by the liquid level stabilization control unit 52 immediately, sothat the liquid level of the liquid solution is drawn to the inside ofthe nozzle 21 (FIG. 14C).

As described above, since the liquid jetting apparatus 20A has effectssimilar to that of the liquid jetting apparatus 20, and the applicationof the jetting pulse voltage to the jetting electrode 28 by the jettingvoltage power source 31A and the application of the driving pulsevoltage of the first voltage value to the piezo element 41 by thedriving voltage power source 42 are performed in synchronization witheach other by the second jetting control unit 51A, jettingresponsiveness can be further improved in comparison to the case ofapplying them at different timings.

[Others]

In the above liquid jetting apparatuses 20, 20A, the piezo element 41 isutilized to form the convex meniscus at the edge portion of the nozzle21, however, as the convex forming section, each section such as forguiding liquid solution to the edge portion side in the in-nozzlepassage 22, flowing to the same direction, increasing the pressure andthe like can also be used. For example, it is possible to form theconvex meniscus by changing the capacity of the inside of the liquidsolution room by an electrostatic actuator system in which a vibrationplate provided in the liquid solution room is deformed, however, this isnot shown in the drawing. Here, the electrostatic actuator is amechanism in which a wall of a passage is deformed by an electrostaticforce to change the capacity. In the case of using the electrostaticactuator, forming the convex meniscus is performed such that theelectrostatic actuator changes the capacity in the liquid solution roomby the shape change thereof to increase the nozzle pressure. Further,when drawing the liquid level at the nozzle edge portion to the inside,it is performed such that capacity of the liquid solution room ischanged by the shape change of the electrostatic actuator, and thenozzle pressure is decreased. By forming the convex meniscus by changingthe capacity with the use of the electrostatic actuator, although thestructure may be complicated compared to the case of using a piezoelement, similarly, there is no limitation to the liquid solution and itis possible to drive at high frequency. In addition, effects ofarranging nozzles with high density and excellent environmentalresponsiveness can be obtained.

Further, as shown in FIG. 15, a heater 41B may be provided in the liquidsolution room of the nozzle plate 26 or near the liquid solution room asa section to heat the liquid solution. This heater 41B rapidly heats theliquid solution and generates air bubbles by evaporation to increase thepressure in the liquid solution room 24, thereby forming the convexmeniscus at the edge portion of the nozzle 21.

In this case, the lowermost layer of the nozzle plate 26 (a layer inwhich the heater 41B is embedded in FIG. 15) needs to have insulatingproperties, however, the structure is not needed to be flexible becausea piezo element is not used. But, when the heater 41B is arranged to beexposed to the liquid solution in the liquid solution room 24, theheater 41B and the wiring thereof need to be insulated.

In principle of the convex meniscus formation, the heater 41B cannotdraw the liquid level of the liquid solution at the edge portion of thenozzle 21, so that the control by the liquid level stabilization controlunit 52 cannot be performed. However, for example as shown in FIG. 16C,the meniscus standby position (the liquid level position of the liquidsolution at the edge portion of the nozzle 21 when the heater 41B doesnot perform heating) is lowered, so that the effect of stabilizing themeniscus just after jetting can be similarly obtained.

The heater 41B with high heat responsiveness is used, and a drivingvoltage power source 42B for applying a heating pulse voltage (forexample, 10 [V]) to the heater 41B is used to drive it.

Further, explaining the operation in the case of adopting the heater 41Bto the liquid jetting apparatus 20, the liquid solution is supplied tothe in-nozzle passage 22, and the jetting voltage is applied to bealways constant to the jetting electrode 28 from the direct currentpower source 30. In this state, the liquid solution is in a chargedstate. The heater 41B is not in a heating state, so that the liquidlevel at the edge portion of the nozzle 21 is at the meniscus standbyposition (FIG. 17A).

Then, when a jetting instruction signal is input to the operationcontrol section 50 from outside, according to the first jetting controlunit 51, the heating pulse voltage by the driving voltage power source42B is applied to the heater 41B. Thereby, air bubbles are generated inthe liquid solution room 24 and the internal pressure thereoftemporarily increases, so that the convex meniscus is formed at the edgeportion of the nozzle 21. Meanwhile, since the liquid solution hasalready been applied with the jetting voltage to be in the chargedstate, the formation of the convex meniscus functions as a trigger tojet a minute droplet from the top thereof (FIG. 17B).

After jetting the droplet, although the convex meniscus becomes in avibration state, the heater 41B is not in a heating state, thus, theliquid level at the edge portion of the nozzle 21 returns to themeniscus standby position. Thus, the convex meniscus disappears and theliquid level of the liquid solution is drawn to the inside of the nozzle21.

As described above, when the convex meniscus forming section has astructure of adopting the heater 41B, the applying voltage to the liquidsolution does not change, so that improvement of responsiveness atjetting and stabilization of liquid volume can be achieved. Further,jetting of the liquid solution can be performed with responsivenessaccording to heat responsiveness of the heater 41B, thereby improvingresponsiveness of the jetting operation.

Since the structure in which the liquid solution room 24 is flexiblelike the case of using a piezo element is not needed, productivity canbe improved due to the simplified structure.

The above heater 41B may be adopted to the liquid jetting apparatus 20A.In this case, when a jetting instruction signal is input from outside bythe second jetting control unit 51A of the operation control section 50Ain a state of continuously applying the bias voltage by the bias powersource 30A, the applications of the jetting pulse voltage by the jettingvoltage power source 31A and the heating pulse voltage by the drivingvoltage power source 42B are performed in synchronization with eachother by the second jetting control unit 51A of the operation controlsection 50A.

In this case, also the applications of the jetting pulse voltage by thejetting voltage power source 31A to the jetting electrode 28 and theheating pulse voltage to the heater 41B by the driving voltage powersource 42B are performed in synchronization with each other, so thatjetting responsiveness can be improved in comparison to the case ofapplying them at different timings.

[Comparative Study]

The results of the comparative study of various liquid jettingapparatuses comprising the above mentioned convex meniscus formingsection and a liquid jetting apparatus with no convex meniscus formingsection performed under the predetermined conditions are explainedbelow. FIG. 19 is a chart showing comparative study results. Thesubjects for the comparative study are seven kinds shown in thefollowing.

{circle around (1)} Control Pattern A

Convex Meniscus Forming Section: Unavailable

Jetting Voltage Applying Section: Bias Voltage+Jetting Pulse Voltage

Synchronization: Unavailable

Liquid Level Sucking: Unavailable

{circle around (2)} Control Pattern B

Convex Meniscus Forming Section: Piezo Element

Jetting Voltage Applying Section: Direct Current Voltage

Synchronization: Unavailable

Liquid Level Sucking: Unavailable

{circle around (3)} Control Pattern C

Convex Meniscus Forming Section: Piezo Element

Jetting Voltage Applying Section: Bias Voltage+Jetting Pulse Voltage

Synchronization: Synchronizing Piezo Element with Jetting Pulse Voltage

Liquid Level Sucking: Unavailable

{circle around (4)} Control Pattern D

Convex Meniscus Forming Section: Piezo Element

Jetting Voltage Applying Section: Direct Current Voltage

Synchronization: Unavailable

Liquid Level Sucking: Available

{circle around (5)} Control Pattern E

Convex Meniscus Forming Section: Piezo Element

Jetting Voltage Applying Section: Bias Voltage+Jetting Pulse Voltage

Synchronization: Synchronizing Piezo Element with Jetting Pulse Voltage

Liquid Level Sucking: Available

{circle around (6)} Control Pattern F

Convex Meniscus Forming Section: Heater

Jetting Voltage Applying Section: Direct Current Voltage

Synchronization: Unavailable

Liquid Level Sucking: Unavailable

{circle around (7)} Control Pattern G

Convex Meniscus Forming Section: Heater

Jetting Voltage Applying Section: Bias Voltage+Jetting Pulse Voltage

Synchronization: Synchronizing Heater with Jetting Pulse Voltage

Liquid Level Sucking: Unavailable

The structure other than the above described conditions is same as thatin the liquid jetting apparatus 20 shown in the first embodiment. Thatis, the nozzle with the inside diameter of the in-nozzle passage and thejetting opening of 1 [μm] is used.

Further, as the driving conditions, frequency of the pulse voltage as atrigger for jetting: 1 [kHz], and the jetting voltage: (1) the directcurrent (400 [V]), (2) the bias voltage (300 [V])+the jetting pulsevoltage (100 [V]), the piezo element driving voltage: 10 [V] and theheater driving voltage 10 [V].

The liquid solution is water, and properties thereof are such that aviscosity: 8 [cP] (8×10⁻² [Pa/S]), a resistivity: 10⁸ [Ωcm] and asurface tension: 30×10⁻³ [N/m].

The evaluation method is performed so that jetting is performed 20 timescontinuously with the above jetting frequency on the glass plate of 0.1[mm]. The evaluation was performed on five scales, wherein five is thebest result.

According to the results of the evaluation, the liquid jetting apparatusof {circle around (5)} Control Pattern E (using the piezo element,applying the superimposed voltage of the bias voltage and the jettingpulse voltage by the jetting voltage applying section, synchronizing thepiezo element with the jetting pulse voltage, and sucking the liquidlevel) shows the highest responsiveness. Incidentally, the controlpattern E is the structure same as the liquid jetting apparatus 20Ashown in the second embodiment.

[Theoretical Description of Liquid Jetting by Liquid Jetting Apparatus]

Hereinafter, a theoretical description of liquid jetting of the presentinvention and a description of a basic example based on this will bemade. In addition, all the contents such as a nozzle structure, materialof each part and properties of jetted liquid, a structure added aroundthe nozzle, a control condition regarding a jetting operation and thelike in the theory and the basic example described hereafter may be,needless to say, applied in each of the above-mentioned embodiments asmuch as possible.

(Approach to Realize Applying Voltage Decrease and Stable Jetting ofMinute Droplet Amount)

Previously, jetting of a droplet with exceeding a range determined bythe following conditional equation was considered impossible.

$\begin{matrix}{d < \frac{\lambda_{c}}{2}} & (4)\end{matrix}$where, λ_(c) is growth wavelength [m] at liquid level of the liquidsolution for making it possible to jet a droplet from the nozzle edgeportion by an electrostatic sucking force, and it can be calculated byλ_(c)=2nγh²/ε₀V².

$\begin{matrix}{d < \frac{{\pi\gamma}\; h^{2}}{ɛ_{0}V^{2}}} & (5) \\{V < {h\sqrt{\frac{\pi\gamma}{ɛ_{0}d}}}} & (6)\end{matrix}$

In the present invention, a role in an electrostatic sucking type inkjetmethod played by the nozzle is reconsidered, in an area where attemptwas not made since it was conventionally regarded as impossible to jet,it is possible to form a minute droplet by using a Maxwell force or thelike.

An equation for approximately expressing a jetting condition or the likefor the approach to reduce a driving voltage and to realize jetting ofminute droplet amount in this way is derived and therefore describedhereafter.

Descriptions hereafter can be applied to the liquid jetting apparatusdescribed in each of the above-mentioned embodiments of the presentinvention.

Assuming that conductive liquid solution is filled to a nozzle of aninside diameter d and the nozzle is perpendicularly placed with a heighth with respect to an infinite plane conductor as a base material at thismoment. This state is shown in FIG. 20. At this time, it is assumed thatelectric charge induced at the nozzle edge portion is concentrated to ahemisphere portion of the nozzle edge, and is approximately expressed inthe following equation.Q=2πε₀αVd  (7)where, Q: electric charge induced at the nozzle edge portion [C], ε₀:electric constant [F/m], h: distance between nozzle and base material[m], d: diameter of inside of the nozzle [m], and V: total voltageapplied to the nozzle [V]. α: proportionality constant dependent on anozzle shape or the like, taking around 1 to 1.5, especially takesapproximately 1 when d<<h.

Further, when the base plate as the base material is a conductive baseplate, it is considered that an image charge Q′ having opposite sign isinduced to the symmetrical position in the base plate. When the baseplate is insulating material, similarly an image charge Q′ of oppositesign is induced to the symmetrical position determined by aconductivity.

By the way, electric field intensity E_(loc) [V/m] of the edge portionof convex meniscus at the nozzle edge portion is, when a curvatureradius of the convex meniscus is assumed to be R [m], given as

$\begin{matrix}{E_{loc} = \frac{V}{kR}} & (8)\end{matrix}$where k: proportionality constant, though being different depending on anozzle shape or the like, taking around 1.5 to 8.5, and in most casesconsidered approximately 5 (P. J. Birdseye and D. A. Smith, SurfaceScience, 23 (1970) 198-210).

Now, for ease, we assume d/2=R. This corresponds to a state where theconductive liquid solution rises in a hemisphere shape having the sameradius as the nozzle radius according to a surface tension force.

We consider a balance of pressure affecting liquid of the nozzle edge.First, when a liquid area at the nozzle edge portion is assumed to be S[m²], electrostatic pressure is given as

$\begin{matrix}{P_{e} = {{\frac{Q}{S}E_{loc}} \approx {\frac{Q}{\pi\;{d^{2}/2}}E_{loc}}}} & (9)\end{matrix}$From the equations (7), (8) and (9), it is assumed that α=1,

$\begin{matrix}{P_{e} = {{\frac{2\; ɛ_{0}V}{d/2} \cdot \frac{V}{k \cdot {d/2}}} = \frac{8\; ɛ_{0}V^{2}}{k \cdot d^{2}}}} & (10)\end{matrix}$

Meanwhile, when a surface tension of the liquid at the nozzle edgeportion is P_(s),

$\begin{matrix}{P_{s} = \frac{4\gamma}{d}} & (11)\end{matrix}$where, λ: surface tension [N/m].

A condition under which jetting of fluid occurs is, since it is acondition where the electrostatic pressure exceeds the surface tension,given as.P_(e)>P_(s)  (12)

By using a sufficiently-small nozzle diameter d, it is possible to makethe electrostatic pressure exceed the surface tension.

According to this relational equation, when a relation between V and dis calculated,

$\begin{matrix}{V > \sqrt{\frac{\gamma\;{kd}}{2\; ɛ_{0}}}} & (13)\end{matrix}$gives the minimum voltage of jetting. In other words, from the equation(6) and the equation (13),

$\begin{matrix}{{h\sqrt{\frac{\gamma\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2\; ɛ_{0}}}} & (1)\end{matrix}$becomes an operation voltage in the present invention.

Dependency of a jetting limit voltage V_(C) with respect to a nozzle ofa certain inside diameter d is shown in the above-mentioned FIG. 9. Fromthis drawing, when a concentration effect of the electric field by theminute nozzle is considered, the fact that the jetting start voltagedecreases according to the decrease of the nozzle diameter was revealed.

In a case of making a conventional consideration with respect to theelectric field, that is, considering only the electric field which isdefined by a voltage applied to a nozzle and by a distance betweencounter electrodes, as the nozzle becomes smaller, a voltage necessaryfor jetting increases. On the other hand, focusing on local electricfield intensity, due to nozzle miniaturization, it is possible todecrease the jetting voltage.

The jetting according to electrostatic sucking is based on charging ofliquid (liquid solution) at the nozzle edge portion. Speed of thecharging is considered to be approximately around time constantdetermined by dielectric relaxation.

$\begin{matrix}{\tau = \frac{ɛ}{\sigma}} & (2)\end{matrix}$where, ε: dielectric constant of liquid solution [F/m], and σ: liquidsolution conductivity [S/m]. When it is assumed that dielectric constantof the liquid solution is 10 F/m, and liquid solution conductivity is10⁻⁶ S/m, τ=1.854×10⁻⁶ sec is obtained. Alternatively, when a criticalfrequency is set to f_(c)[Hz],

$\begin{matrix}{f_{c} = \frac{\sigma}{ɛ}} & (14)\end{matrix}$is obtained. It is considered that jetting is impossible because it isnot possible to react to the change of the electric field having fasterfrequency than this f_(c). When estimation regarding the above-mentionedexample is made, the frequency takes around 10 kHz. At this time, in acase of a nozzle radius of 2 μm and a voltage of a little under 500V, itis possible to estimate that current in the nozzle G is 10⁻¹³ m³/s. In acase of the liquid of the above-mentioned example, since it is possibleto perform the jetting at 10 kHz, it is possible to achieve minimumjetting amount at one cycle of around 10 fl (femto liter, 1 fl=10⁻¹⁶ l).

In addition, each of the above-mentioned embodiments, as shown in FIG.20, is characterized by a concentration effect of the electric field atthe nozzle edge portion and by an act of an image force induced to thecounter base plate. Therefore, it is not necessary to have the baseplate or a base plate supporting member electrically conductive asconventionally, or to apply a voltage to these base plate or base platesupporting member. In other words, as the base plate, it is possible touse a glass base plate being electrically insulated, a plastic baseplate such as polyimide, a ceramics base plate, a semiconductor baseplate or the like.

Further, in each of the above-mentioned embodiments, the applyingvoltage to an electrode may be any of plus or minus.

Further, by maintaining a distance between the nozzle and the base platenot more than 500 [μm], it is possible to make the jetting of the liquidsolution easy. Further, preferably, the nozzle is maintained constantwith respect to the base material by doing a feedback control accordingto a nozzle position detection.

Further, the base material may be mounted on a base material holderbeing either electrically conductive or insulated to be maintained.

FIG. 21 shows a side sectional view of a nozzle part of the liquidjetting apparatus as one example of another basic example of the presentinvention. At a side surface portion of a nozzle 1, an electrode 15 isprovided, and a controlled voltage is applied between the electrode 15and an in-nozzle liquid solution 3. The purpose of this electrode 15 isan electrode for controlling Electrowetting effect. When a sufficientelectric field covers an insulator structuring the nozzle, it isexpected that the Electrowetting effect occurs even without thiselectrode. However, in the present basic example, by doing the controlusing this electrode more actively, a role of a jetting control is alsoachieved. In the case that the nozzle 1 is structured from insulator, anozzle tube at the nozzle edge portion is 1 μm, a nozzle inside diameteris 2 μm and an applying voltage is 300V, it becomes Electrowettingeffect of approximately 30 atmospheres. This pressure is insufficientfor jetting but has a meaning in view of supplying the liquid solutionto the nozzle edge portion, and it is considered that control of jettingis possible by this control electrode.

The above-mentioned FIG. 9 shows dependency of the nozzle diameter ofthe jetting start voltage in the present invention. As the nozzle of theliquid jetting apparatus, one which is shown in FIG. 11 is used. As thenozzle becomes smaller, the jetting start voltage decreases, and thefact that it was possible to perform jetting at a lower voltage thanconventionally was revealed.

In each of the above-mentioned embodiments, conditions for jetting theliquid solution are respective functions of: a distance between nozzleand base material (h); an amplitude of applying voltage (V); and anapplying voltage frequency (f), and it is necessary to satisfy certainconditions respectively as the jetting conditions. Adversely, when anyone of the conditions is not satisfied, it is necessary to changeanother parameter.

This state will be described with reference to FIG. 22.

First, for jetting, a certain critical electric field E_(c) exists,where jetting is not performed unless the electric field is not lessthan the electric field E_(c). This critical electric field is a valuechanged according to the nozzle diameter, a surface tension of theliquid solution, viscosity or the like, and it is difficult to performthe jetting when the value is not more than E_(c). At not less than thecritical electric field E_(c), that is, at jetting capable electricfield intensity, approximately a proportional relation arises betweenthe distance between nozzle and base material (h) and the amplitude ofapplying voltage (V), and when the distance between nozzle and basematerial is shortened, it is possible to make the critical applyingvoltage V smaller.

Adversely, when the distance between nozzle and base material h is madeextremely apart for making the applying voltage V larger, even if thesame electric field intensity is maintained, according to an effect suchas corona discharge or the like, blowout of fluid droplet, that is,burst occurs.

INDUSTRIAL APPLICABILITY

As described above, the present invention is suitable to jet a dropletfor each usage of normal printing as graphic use, printing to specialmedium (film, fabric, steel plate), curved surface printing, and thelike, or patterning coating of wiring, antenna or the like by liquid orpaste conductive material, coating of adhesive, sealer and the like forprocessing use, for biotechnological, medical use, pharmaceuticals (suchas one mixing a plurality of small amount of components), coating ofsample for gene diagnosis or the like.

1. A liquid jetting apparatus to jet a droplet of a charged liquidsolution onto a base material, comprising: a liquid jetting headcomprising a nozzle to jet the droplet from an edge portion, an insidediameter of the edge portion of the nozzle being more than 0.2 μm andbeing not more than 4 μm, the nozzle being integrally formed with anozzle plate; a liquid solution supplying section to supply the liquidsolution into the nozzle; a jetting voltage applying section to apply ajetting voltage to the liquid solution in the nozzle, the jettingvoltage applying section comprising a jetting electrode provided as alayer on a back end surface of the nozzle plate, the jetting electrodehaving an ink passage hole positioned at a border between the liquidsolution supplying section and the inside passage; and a convex meniscusforming section to form a state where the liquid solution in the nozzleprotrudes from the nozzle edge portion; wherein the jetting voltage isset to a value in the range that a droplet is capable of being jetted ina state where a convex meniscus by the liquid solution is formed at theedge portion of the nozzle, and a droplet is not jetted in a state wherethe convex meniscus is not formed.
 2. The liquid jetting apparatus ofclaim 1, further comprising an operation control section to control anapplication of a driving voltage for driving the convex meniscus formingsection and an application of the jetting voltage by the jetting voltageapplying section, wherein the operation control section comprises afirst jetting control unit to control the application of the drivingvoltage of the convex meniscus forming section when jetting a dropletwhile controlling the application of the jetting voltage by the jettingvoltage applying section.
 3. The liquid jetting apparatus of claim 2,wherein the operation control section comprises a liquid stabilizationcontrol section to perform an operation control to draw a liquid levelat the nozzle edge portion to an inside after the protruding operationof the liquid solution and the application of the jetting voltage. 4.The liquid jetting apparatus of claim 1, further comprising an operationcontrol section to control a driving of the convex meniscus formingsection and a voltage application by the jetting voltage applyingsection, wherein the operation control section comprises a secondjetting control unit to perform a protruding operation of the liquidsolution by the convex meniscus forming section and an application ofthe jetting voltage in synchronization with each other.
 5. The liquidjetting apparatus of claim 4, wherein the operation control sectioncomprises a liquid stabilization control section to perform an operationcontrol to draw a liquid level at the nozzle edge portion to an insideafter the protruding operation of the liquid solution and theapplication of the jetting voltage.
 6. The liquid jetting apparatus ofclaim 1, wherein the convex meniscus forming section comprises a piezoelement to change a capacity in the nozzle.
 7. The liquid jettingapparatus of claim 1, wherein the convex meniscus forming sectioncomprises a heater to generate an air bubble in the liquid solution inthe nozzle.
 8. The liquid jetting apparatus of claim 1, wherein ajetting voltage V by the jetting voltage applying section satisfies thefollowing equation (1); $\begin{matrix}{{h\sqrt{\frac{\gamma\pi}{ɛ_{0}d}}} > V > \sqrt{\frac{\gamma\;{kd}}{2\; ɛ_{0}}}} & (1)\end{matrix}$ where, γ: surface tension of liquid solution [N/m], ε₀:electric constant [F/m], d: nozzle diameter [m], h: distance betweennozzle and base material [m], k: proportionality constant dependent onnozzle shape (1.5<k<8.5).
 9. The liquid jetting apparatus of claim 1,wherein the nozzle is formed with a material having an insulatingproperty which indicates dielectric breakdown strength of not less than10 kV/mm.
 10. The liquid jetting apparatus of claim 1, wherein at leastthe edge portion of the nozzle is formed with a material having aninsulating property which indicates dielectric breakdown strength of notless than 10 kV/mm.
 11. The liquid jetting apparatus of claim 1, whereinthe liquid solution supplying section comprises a liquid solution room,and the ink passage hole is at a border position between the liquidsolution room and the inside passage of the nozzle.
 12. The liquidjetting apparatus of claim 1, wherein the inside diameter of the nozzleat the nozzle edge portion and an inside diameter of the inside passageof the nozzle are uniform.